In the case of Nuclear and Electron Spin Resonance Spectroscopy, a high frequency signal is obtained as a result of the excitation of the sample which is to be analyzed. This is an interference signal formed by the sum of various oscillations of different frequency and amplitude. The frequencies and amplitudes of the individual components of the interference signal, also called interferogram, can be obtained by executing a Fourier-analysis. This Fourier-analysis can be performed by digital data processing provided that the interferogram is stored as a sequence of digital words, whch specify the amplitude of the interferogram at discrete time intervals. The time interval between amplitude values determines the highest frequency which can be measured. The analysis of very weak signals may require many repetitions of the measuring procedure with the addition of the signals obtained. In this way, even those signals can be recognized which are normally below the noise level. This, however, requires an absolutely phase-coherent addition of the amplitude values obtained during successive measurements. The data quantities resulting from such measurements are too large to allocate them to a main memory with random access. It is possible, for example, that there are 128 K words (K=1024) with 24 bits each during such a measurement.
Due to the large amount of data to be processed, there are known devices on the market for digital accumulation, storage and processing of data signals in connection with spin resonance and infrared spectrometers, which devices utilize, in addition to the main memory with random access, a disk storage system for accumulating the main part of the data. After the main memory has accumulated a certain number of data words delivered by the A/D converter, these words are transferred to the disk storage as a word block. The main memory offers place for two such word blocks and thus enables, on the one hand, the continuous input of words into one of these blocks and, on the other hand, the transfer of words from the second block to the disk storage. Furthermore, it is possible to back-transfer words resulting from a preceding measurement from disk into the main memory in order to to perform a summation of such back-transferred words with corresponding words created during another measurement.
The transfer of words from the A/D converter to the main memory is performed by a data channel containing a pointer register and a word counter. At the beginning of a measuring procedure, the pointer register is loaded with the address in the main memory where the first word of a word block must be stored. The word counter is loaded with the number of words contained in a word block. The appropriate register values are loaded by the central unit. After the measuring procedure is started, the data acquisition and data transfer to the main memory are performed independently of the central unit, such that the A/D converter processes the incoming signal at specified time intervals to give digital words which are transferred to the main memory via an addressing matrix and placed into the addresses determined by the pointer register. During every word transfer the contents of the pointer register and the word counter are modified until the desired number of words defined by the initial contents of the word counter have been transferred. At this point, the word counter informs the central unit that the word block is complete. Now, the central unit determines whether a further word block is to be processed or not. In the first case, the pointer registers and the word counter are loaded again and the data transfer will continue. In the latter case, a completely new measuring procedure may be started or the procedure is terminated.
The rate at which the interferogram is converted to digital words determines the highest frequency component that can be resolved by the following Fourier-analysis. For recognizing signal components of high frequency a very high scanning rate is desired. On the other hand, the scanning rate is limited by the time required for data processing and especially for data storage. One of the limiting factors is the duration necessary to transfer the data from the main memory to the disk storage and vice versa. Here, the operation speed of the disk storage is of great importance. The time interval allowed between successive data words assigned to any individual word block must be absolutely the same etime interval used in the following subsequent word blocks. Furthermore, the change from one data block to another must be performed in exactly this same time interval. For this reason, the time interval between two words must be chosen large enough to guarantee the transfer of a word block from the main memory to the disk storage and vice versa within the time necessary for accumulating another word block. A further condition is that between accumulating two words the central unit can fulfil the controlling tasks necessary during the transfer from one word block to the other. As far as the known devices are concerned, the central unit interrupts its actual activity for testing the operation status when the word counter sends the corresponding signal and transmits new data to the pointer register and the word counter. Depending on what tasks the central unit has to carry out, this interruption may require the processing of a long routine and the following activity might be interrupted by requirements of higher priority. Finally, the necessary tests and transfers of data require a large number of memory cycles, so that a considerable time may pass after the transfer of the last word of a word block until all measures are taken in order to transfer the first word of the following words block into the main memory.
As far as the above-mentioned known devices are concerned, the limiting factor is the disk storage, Here, it must be taken into account for reasons of cost that the devices of the type in question only will allow the use of relatively simple disk storage units. At the moment, however, economical disk storage devices are available having a considerably higher operation speed. The factor limiting the data acquisition is the time required by the central unit for controlling the transfer from one word block to the other. Attempts to reduce this time by a special time-saving programming turned out to be unsuccesful.